The nature of bone cell calcium regulation will be studied directly using isolated bone cells. Cells will be isolated by collagenase digestion of 20-21 day old fetal rat calvaria. Ca-ATPase involvement in calcium efflux will be studied with bone cell membranes. A possible relationship of sodium and calcium transport will be investigated by studying the effect of various extracellular/intracellular ratios of sodium on Ca45 uptake and efflux. The effects of calcitonin and 1,25 dihydroxycholecalciferol on calcium transport will also be studied. The information obtained in this study should aid in the understanding of the mechanism of action of calcitonin and 1.25 dihydroxycholecalciferol as well as provide basic information about bone cell calcium regulation.